Optical switch mechanism

ABSTRACT

An optical switching mechanism including a vibrator having a pair of parallel reeds which are sustained in vibration at a rate determined by the resonance characteristic of the vibrator, the free ends of the reeds being ganged together by a headpiece. The arrangement is such that as the reeds sway simultaneously from side to side, the headpiece is caused to undergo a translating movement substantially free of an arcuate component. Mounted on the headpiece is a triangular reflecting element whose apex, in the static state of the vibrator, is aligned with a beam of incident radiant energy, whereby as the element, in the dynamic state, shifts to either side of the beam, the beam is deflected by the angled faces of the element in alternate directions.

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[54] OPTICAL SWITCH MECHANISM [72] Inventors: Frank Dostal; CharlesBadowski,

both of New York, NY.

[73] Assignee: Bulova Watch Company, Inc., New

York, NY.

[22] Filed: Aug. 3, 1970 21' Appl. No.: 60,249-

[52] US. Cl. ..350/6, 73/702, 350/285, 324/80 [51] Int. Cl. ..G02b 17/00[58] Field of Search ..350/6, 7, 162, 285, 288; 178/7.6; 73/702; 324/80[56] References Cited UNITED STATES PATENTS 1,438,974 12/1922 Wente..350/6 3,549,244 12/1970 Shaffer ..350/6 2,920,529 1/ 1960 Blythe..350/285 3,087,373 4/1963 Poor et a1. ..350/7 Primary Examiner-DavidSchonberg Assistant Examiner-Michael J. Tokar Attorney-Michael Ebert[57] ABSTRACT An optical switching mechanism including a vibrator havinga pair of parallel reeds which are sustained in vibration at a ratedetermined by the resonance characteristic of the vibrator, the freeends of the reeds being ganged together by a headpiece. The arrangementis such that as the reeds sway simultaneously from side to side, theheadpiece is caused to undergo a translating movement substantially freeof an arcuate component. Mounted on the headpiece is a triangularreflecting element whose apex, in the static state of the vibrator, isaligned with a beam of incident radiant energy, whereby as the element,in the dynamic state, shifts to either side of the beam, the beam isdeflected by the angled faces of the element in alternate directions.

9 Claims, 14 Drawing Figures Patented Oct. 24, 1972 2 Sheets-Sheet 1 5an m E 4 mm .1 W m w A/ A F3 m m H Wm M w m m 13y humus Seamus OPTICALSWITCH MECHANISM BACKGROUND OF THE INVENTION This invention relatesgenerally to optical switching devices, and more particularly to adevice in which an optical reflecting element is mounted on a mechanicalresonator and is adapted to direct an incident beam in alternatedirections.

Various forms of optical devices are currently in use to chop, pulse,scan, sweep or otherwise modulate a beam of radiant energy. Such devicesare incorporated in mass spectrometers, bolometers, star trackers,colorimeters, horizon sensors and in various instruments which utilizeor analyze nuclear, X-Ray or laser beams, or beams in the visible,ultra-violet or infra-red region.

Existing optical devices for this purpose usually make use ofmotor-driven discs, drums, mirrors or prisms. Devices using motors arerelatively big and heavy, and have large power requirements,particularly at higher frequencies, thus necessitating extra size andweight provisions for inverters or similar power supplies. Also in useare electromagnetically actuated armature devices in which the pivotedarmature is mounted on jeweled bearings. Optical modulators of thesetypes are relatively inefficient and unstable. Moreover, they arelacking in shock resistance, they inevitably produce jitter due tomicroscopic shake or rattle at their bearings, and they have otherdrawbacks which limit their usefulness.

It is also known to use resonant tuning forks to vibrate opticalelements, and while such forks overcome many of the drawbacks found inmotor-driven choppers, they are comparatively expensive and are unableto produce large angular excursions of the optical elements whenoperated at low power.

The primary concern of the present invention is beam-switchingmechanisms; that is, mechanisms adapted to direct a beam of incidentradiant energy such as a beam of monochromatic radiation or a laser ray,in alternate paths. One available form of mechanism for this purpose isa motor-driven disc bearing multiple mirrors which are arranged toreflect an incident beam in alternative directions. But, as pointed outabove, motor-driven optical devices are cumbersome and have relativelylarge power requirements.

Another approach to the problem is to make use of a reflecting mirrorborne on the tine of a vibrating tuning fork. But, because the tine, inswinging from side to side, operates within an arc, this results in anangular motion of the mirror and gives rise to undesirable smearing ofthe reflected beam to produce an unwanted scanning action. This drawbackis aggravated with large mirror angles as well as at increasing forkamplitudes.

SUMMARY OF THE INVENTION In view of the foregoing, it is the primaryobject of this invention to provide an improved optical switchingmechanism which functions to deflect a beam of radiant energy inalternate directions.

More specifically, it is an object of the invention to provide amechanism of the above type which utilizes a double reed adapted toreciprocate a reflecting element from side to side without anaccompanying arcuate component of motion.

Also an object of the invention is to provide a vibrating mechanism ofthe double-reed type which is characterized by high optical efficiencyin that virtually all of the beam energy is utilized in the course ofswitching, no significant portion of the incident beam being omittedfrom the alternate reflecting paths.

Still another object of the invention is to provide an optical switchingmechanism which is compact, lightweight, and has exceptionally low powerrequirements, in the order of milliwatts.

Briefly stated, these objects are attained in an optical switchingmechanism including a vibrator having a pair of parallel reeds whosefree ends are ganged together by a headpiece whereby, as the drivenreeds are caused to swing simultaneously from side to side, theheadpiece is caused to undergo a translational movement substantiallyfree of an arcuate component of motion. Mounted on the headpiece is areflecting element having a triangular formation defined by an apex andangled faces, the apex, in the static state, being aligned with anincident beam of radiant energy whereby, as the element vibrates, thebeam alternately strikes the faces and is reflected thereby.

OUTLINE OF DRAWING For a better understanding of the invention, as wellas other objects and further features thereof, reference is made to thefollowing detailed description to be read in conjunction with theaccompanying drawing, wherein:

FIG. 1 is a front elevational view of an optical switching mechanism inaccordance with the invention; FIG. 2 is a side elevational view of themechanism; FIG. 3 is a plan view of the base of the mechanism;

FIG. 4 is a plan view of the reflecting element;

FIG. 5 schematically illustrates the associated electronic drive circuitfor the mechanism;

FIGS. 6A and 6B illustrate the position of the reflecting element andits associated double reed, in the static state;

FIGS. 7A and 7B illustrate the position of the element and itsassociated double reed when deflected to the right;

FIGS. 8A and 8B illustrate the position of the element and itsassociated double reed when deflected to the left;

FIGS. 9A and 9B illustrate the position of the element and itsassociated double reed, in the dynamic state, vibrating to the left andright;

FIG. 10 illustrates a modified form of reflecting element to produceright-angle switching;

FIGS. 11A, 11B, 11C, 11D and 11E illustrate a semicylindrical reflectingelement in perspective, front and plan view, respectively, and invarious vibratory positions;

FIGS. 12A and 128 show an optical element in the form of a light chopperin front and plan view, respectively;

FIG. 13 shows an optical element in the form of an opaque vane acting asa beam chopper; and

FIG. 14 shows an optical element in the form of a vane having a slittherein providing a beam-chopping action.

Referring now to the drawing and more particularly to FIGS. 1 to 4,there is shown an optical switching mechanism in accordance with theinvention, including a vibrator having a pair of identical flexiblereeds and 11, disposed in parallel relation, the feet thereof beinganchored in a base plate 12. For this purpose, base 12, as best seen inFIG. 3, is provided with channels 12A and 12B to accommodate pressureblocks 13 and 14 which are pressed against the respective feet of reeds10 and 11 by set screws 15 and 16.

Reeds 10 and 11 are preferably formed of a flexible metal having a lowtemperature coefficient of expansion to render the vibratorsubstantially insensitive to changes in ambient temperature. Suitablefor this purpose are materials having a high mechanical Q, long fatiguelife and a good temperature/elasticity coefficient, such as Ni-Span C orElinvar.

The free ends of reeds 10 and 11 are ganged together by means of aheadpiece 17 having slots therein to receive the ends, the ends beingsecured to the headpiece by screws 18 and 19. Mounted at correspondingintermediate positions on the reeds and projecting laterally therefromin opposing directions are permanent magnets 20 and 21. Magnet 20 isreceived within a pick-up coil while magnet 21 is received within adrive coil 23, both coils being supported on a back plate 24 mounted onbase 12. The mechanism is housed in a suitable container, only one wall25 of which is shown in FIG. 1.

Mounted above headpiece 17 is a reflecting element 26 having atriangular formation to define an apex 27 and angled mirror faces 26Aand 26B. Reflecting element 26, as will be later explained, functions toswitch an incident beam of radiant energy in alternate directions.

The resonance frequency of the vibrator is determined by the length andstiffness of reeds 10 and 11 as well as by the mass of headpiece 17 andreflecting element 26. Pick-up coil 22, as shown in FIG. 5, is connectedto the input of an amplifier 28, preferably of the solid-state type,whose output is coupled to drive coil 23, the combination of the coilsand amplifier creating a positive feedback system serving to sustain thevibrator in oscillation at its resonance frequency in a wellknownmanner.

In lieu of a pick-up coil and magnet, one may attach a piezoelectriccrystal 29 to one of the reeds to generate the pick-up voltage appliedto the input of amplifier 28. The manner in which the vibrator isexcited and sustained in vibration forms no part of the presentinvention, for any conventional means may be used for this purpose.

Referring now to FIG. 6, reflecting element 26 on the vibrator is shownin the static state. When the element is at rest, its orientation issuch that the beam L from a source of radiant energy is in alignmentwith the optical axis 0 passing through apex 27 of the reflecting element. The diameter of the beam is much smaller than the width of theelement and the rays from the beam are therefore divided between theangled faces 26A or 268 and are reflected thereby in alternate paths Xand Y. The angle between these paths and optical axis 0 depends, ofcourse, on the geometry of the reflecting element.

When the vibrator is excited, the two reeds 10 and 11, which are gangedtogether at their free ends, swing back and forth at a rate determinedby the resonance movement is similar to the head movement of a Siamesedancer whereby, as the neck is caused to sway, the head moves from sideto side without tilting.

Consequently, when reeds 10 and 11 move toward the right, as shown inFIG. 7B, the intermediate portions thereof, which are subjected to anelectromagnetic force, bend toward the right, whereas the feet portionsof the reeds, which are anchored, maintain their stationary positionwhile the reflecting element 26 mounted on headpiece l7 shifts towardthe right without an arcuate component. Thus, beam L, as shown in FIG.7B, now strikes only reflecting face 26A, and all of the beam energy isreflected along path X in the direction of a sensor or detector D ISince the angle of reflection remains constant as the apex is displacedtoward the right, during the entire right stroke of the vibrator, thebeam is reflected without any scanning motion thereof. Similarly, asshown in FIGS. 8A and 8B, when reflecting element 26 translates towardthe left, the entire beam is reflected without scanning motion alongpath Y todetector Dy.

' FIGS. 9A and 9B show a full operating cycle in the course of whichbeam L alternates between paths X and Y to produce light pulses whichare picked up by detectors D x and Dy whose outputs are in square-waveform inasmuch as all beam light is reflected and utilized.

Where a conventional vibrating scanning reflector is used to switch abeam impinging thereon from one direction to another, the reflected beamis intercepted by a detector for a relatively brief interval in thecourse of an operating cycle, for the beam is received only when theangle of the scanning mirror momentarily is in line with the detector.Consequently, with a scanning-type switching system, only a smallportion of the available light or other form of radiant energy isutilized, whereas in the present invention the entire light output isexploited.

Again it must be emphasized that in the present invention, the reflectedbeam is perfectly stationary even though the reflecting element moves.For instance, assuming a laser beam having a 1mm diameter and areflecting element 26 with faces 26A and 268, each of which is 5mmwide,'the peak-to-peak travel band of the reflecting element being 8mm,the reflected beam will remain stationary even though the mirror moves4mm per face.

In some instances, it is desirable to provide rightangle beam-switching.This is accomplished, as shown in FIG. 10, by a reflecting element 26'whose faces 26A and 26B are each displaced 45 relative to the opticalaxis 0. Hence the beam is reflected at right angles to the angle ofincidence and the reflections in paths X and Y are in opposingdirections.

It may also be desirable to provide a reference light pulse betweensuccessive switching pulses. This is accomplished, as seen in FIG. 10,by a flattened transparent apex 27', whereby beam L, at the zeroposition of the vibrator, passes through the reflecting element toproduce a light pulse P at a detector positioned on the optical axis.The square-wave pulses yielded by the detector which intercepts thereflected beam in the X path are represented by pulses P while thoseproduced in the Y path are represented by pulses P the latter being 180out of phase with the former. The spurt of reference light passingthrough the reflector at the transparent apex provides a preciseindication of the zero crossing.

Because the vibrator is adapted to translate an optical element withoutan accompanying scanning motion, one may, by the use of curved mirrors,obtain an optical scanning action. Thus, as shown in FIGS. 11A, B and C,a semicylindrical mirror 30 may be mounted on the vibrator, with thebeam L in the static state of the vibrator, striking the mirror at itsoptical axis 0 which is at 360, the curved face extending to 90 at oneside of the axis and to 270 on the other. Thus at the rest position,beam 11 is reflected back on itself as shown in FIG. 11C. However, asthe mirror shifts to the right (FIG. 11D), beam L is reflected from 360to 270, and as the mirror shifts to the left (FIG. 11E), beam L isreflected from 360 to 90. The total scan, therefore, is 180.

The optical element, as shown in FIGS. 12A and 128, may take the form ofa diffraction grating 31, intercepting light beam L, the grating beingvibrated by ganged reeds and 11. To produce a light-chopping action at arate determined by the frequency of the vibrator, one may use an opticalelement in the form of an opaque vane 32 as shown in FIG. 13, toperiodically intercept beam 1 1.

In FIG. 14, another form of light-chopper is shown, wherein vane 32 hasa slit 33 formed therein. Beam L is chopped twice per vibrating cycle ofthe double-reed vibrator. In this instance, the peak-to-peak motion ofthe vane has to be twice the width of slit 33.

While there have been shown and described preferred embodiments of theinvention, it will be appreciated that many changes and modificationsmay be made therein without departing from the essential spirit of theinvention.

We claim:

1. An optical mechanism for modulating a beam of radiant energy, saidmechanism comprising:

A. a vibrator having a pair of parallel reeds of the same fixed lengthanchored at their feet, and a headpiece ganging together the free endsof the reeds,

B. means to sustain said vibrator in vibration at its resonancefrequency whereby as the reeds swing back and forth, the headpiecethereon is caused to undergo translation without an accompanying arcuatecomponent, and

C. an optical element mounted on said headpiece in a position tointercept said beam.

2. A mechanism as set forth in claim 1, wherein said element is areflector having a triangular formation defined by an apex and a pair ofangled faces, said apex in the static state of the vibrator beingaligned with said beam whereby said beam is alternately reflected bysaid faces when the vibrator is in the dynamic state.

3. A mechanism as set forth in claim 2, wherein said apex is flattenedand transparent to provide reference pulses.

4. A mechanism as set forth in claim 2, wherein said faces are disposedat right angles to each other to cause the beam to be reflected inopposing directions.

5. A mechanism as set forth in claim 1, wherein said reeds areelectromagnetically driven at a point intermediate the free ends and thefeet thereof.

6. A mechanism as set forth in claim 1, wherein said element issemicylindrical to effect a scanning action of a beam incident thereto.

7. A mechanism as set forth in claim 1, wherein said element is adiffraction grating having alternate bands which are opaque andtransparent to produce a scanning or modulating action of a beamincident thereto.

8. A mechanism as set forth in claim 1, wherein said element is a vanefor periodically chopping an incident beam.

9. A mechanism as set forth in claim 8, wherein said vane includes aslit to intercept said beam.

1. An optical mechanism for modulating a beam of radiant energy, saidmechanism comprising: A. a vibrator having a pair of parallel reeds ofthe same fixed length anchored at their feet, and a headpiece gangingtogether the free ends of the reeds, B. means to sustain said vibratorin vibration at its resonance frequency whereby as the reeds swing backand forth, the headpiece thereon is caused to undergo translationwithout an accompanying arcuate component, and C. an optical elementmounted on said headpiece in a position to intercept said beam.
 2. Amechanism as set forth in claim 1, wherein said element is a reflectorhaving a triangular formation defined by an apex and a pair of angledfaces, said apex in the static state of the vibrator being aligned withsaid beam whereby said beam is alternately reflected by said faces whenthe vibrator is in the dynamic state.
 3. A mechanism as set forth inclaim 2, wherein said apex is flattened and transparent to providereference pulses.
 4. A mechanism as set forth in claim 2, wherein saidfaces are disposed at right angles to each other to cause the beam to bereflected in opposing directions.
 5. A mechanism as set forth in claim1, wherein said reeds are electromagnetically driven at a pointintermediate the free ends and the feet thereof.
 6. A mechanism as setforth in claim 1, wherein said element is semicylindrical to effect ascanning action of a beam incident thereto.
 7. A mechanism as set forthin claim 1, wherein said element is a diffraction grating havingalternate bands which are opaque and transparent to produce a scanningor modulating action of a beam incident thereto.
 8. A mechanism as setforth in claim 1, wherein said element is a vane for periodicallychopping an incident beam.
 9. A mechanism as set forth in claim 8,wherein said vane includes a slit to intercept said beam.